First, create a free developer account on this sandbox and request a developer key. You will be asked to submit basic information about your app at this stage. Register here.
Use our SDKs to connect your app to the Open Bank Project APIs. You will need your developer key, which was provided to you when you created an account. See all available APIs on the API Explorer. Please make sure you are using the correct base URL.
Once your app is connected, you can test it using test customer credentials. You can find a list of sandbox customer logins HERE.